Module 2 Flashcards
What’s in the centre of an atom?
protons and neutrons which make up the nucleus
What orbits the nucleus?
electrons in shells
give the relative mass of all subatomic particles
proton=1
neutron=1
electron=1/2000
give the relative charges of all subatomic particles
proton= +1
neutron= 0
electron =-1
atomic number?
number of protons.
also number of electrons if not charged
mass number?
number of protons and neutrons in nucleus
isotope?
atoms of the same element with different numbers of neutrons
what do isotopes of the same element have?
- different masses
- same number of protons and electrons
- different numbers of neutrons in nucleus
why do different isotopes of the same element react in the same way?
because:
- it’s the number and arrangement of electrons that decides the chemical properties of an element and isotopes have the same configuration so the same chemical properties.
- neutrons make no difference to chemical reactivity
what are ions?
an ion is a positively or negatively charged atom or (covalently bonded) group of atoms (a molecular ion)
You have an Na+ ion. Give the atomic number Give the mass number Give proton Give neutron Give electron Overall charge?
atomic no =11 mass no=23 p=11 n=12 e=10 overall charge=11-10=1+
You have a Cl- ion. Give the atomic number Give the mass number Give proton Give neutron Give electron Overall charge?
atomic no =17 mass no=35 p=17 n=18 e=18 overall charge= 17-18= 1-
F- is a negative ion
Explain
The negative charge means there’s 1 more electron than there are protons. F has 9 protons so F- must have 10 electrons. The overall charge = +9-10= -1
Mg2+ is a positive ion.
Explain.
The 2+ charge means that there are 2 fewer electrons than there are protons. Mg has 12 protons so Mg2+ must have 10 electrons. The overall charge = +12-10=+2
What did Democritus say about matter?
All matter is made from indivisible particles
What did John Dalton say about matter?
described atoms as solid spheres and that different types of sphere made up different elements
What did JJ Thomson say about matter
1897
-atoms weren’t solid and indivisible
-atom must contain a smaller negatively charged particle “corpuscles” (electrons) so the solid sphere idea of atomic structure had to be changed.
NEW MODEL PLUM PUDDING - A POSITIVELY CHARGED SPHERE WITH NEGATIVE ELECTRONS EMBEDDED IN IT
What did Rutherford say about matter?
1909 Rutherford Geiger and Marsden gold foil experiment.
there’s a tiny positively charged nucleus at the centre of the atom surrounded by a “cloud” of negative electrons. Most of the atoms mass is concentrated at the centre so most of the atom is empty space.
Further Modifications to Rutherford model?
Henry Moseley discovered the charge of the nucleus increased from one element to another in units of one.
Rutherford discovered that the nucleus contained positively charged particles called proton.
The charges of the nucleus of different atoms could be explained because atoms of different elements have a different number of protons in their nucleus
James Chadwick on atomic models
the nucleus of atoms were heavier if they just contained protons
Rutherford predicted there were other particles in the nucleus with mass but no charge
James Chadwick discovers the neutron
Describe in 4 steps, Bohrs atomic model
Niels Bohr:
- Electrons only exist in fixed orbits(shells) and not anywhere in between
- Each shell has a fixed energy
- When an electron moves between shells electromagnetic radiation is emitted or absorbed
- because the energy of shells is fixed, the radiation will have a fixed frequency
What else did the Bohr model explain?
The Bohr model also explained why the noble gases are inert.
He said the shells of an atom can only hold fixed numbers of electrons and an elements reactivity is due to its electrons.
So when an atom has full shells of electrons it’s stable and does not respect.
What’s the most accurate atomic model today?
Involves quantum mechanics- you can never know where an electron is or which direction it’s going in at any moment, but you can say how likely it is to be at a certain point in the atom.
Electrons can act as waves as well as particles.
DEFINE relative atomic mass Ar
The weighted mean mass of an atom of an element compared to 1/12 of the mass of an atom of carbon 12 the relative atomic mass of each element is shown in the periodic table.
DEFINE relative isotopic mass
relative isotopic mass is the mass of an atom of an isotope of an element compared to 1/12 of the mass of an atom of carbon 12.
How is relative atomic mass (Ar) of an element calculated from its isotopic abundance’s?
- multiply each relative isotopic mass by its % relative isotopic abundance
- /100
Get a calculator.
Calculate the Ar of boron:
20% of boron atoms have a relative isotopic mass of 10.0 while 80% have a relative isotopic mass of 11.0.
-multiply each relative isotopic abundance and add up the results:
(10.0x20.0) + (80.0x11.0) = 200+880 =1080
divide by 100: 10.8
What is mass spectrometry?
What’s a mass spectrum?
- form of molecular chemical analysis, ions passed through mass spectrometer, ions sorted based on their mass-to-charge ratio.
- a mass spectrum is produced, can be used to identify an unknown compound, provides structural information about the molecule - can determine the relative abundance of each isotope of an element.
VIADD
1. Vaporisation - sample is vaporised before being injected into the mass spectrometer
- Ionisation - vaporised sample is bombarded with electrons in the ionisation chamber
- electrons knock electrons out of the sample
- positive ions are formed
- majority of ions carry +1 charge - Acceleration- beam of ions is accelerated
- Deflection- magnetic field deflects the beam, different ions are deflected by different amounts, degree of deflection depends on mass and charge (lighter ions deflected more and those which carry a bigger charge are deflected more)
- Detection- not all of the ions will reach the detector, some ions may: collide with walls of mass spec, gain electrons and become neutralised. Those that do reach the detector are detected as an electric current, electricity flows when ion hits metal detector box so allows detection of ions.
on a mass spectrum:
y axis?
x axis?
y= abundance of ions often as a %, for an element the height of each peak gives the relative isotopic abundance
x= units given as a mass/charge ratio
add mass spectra example
pic
DEFINE relative molecular mass Mr
The average mass of a molecule compared to 1/12 of the mass of an atom of carbon 12.
To find the Mr just add up the relative atomic mass values of all the atoms in the molecule
Calculate the relative molecular mass of C2H6O
Mr of c2h6o = (2x12) + (6x1) + (1x16) = 46
DEFINE relative formula mass.
Relative formula mass is the average mass of a formula unit compared to 1/12 of the mass of an atom of carbon 12.
It’s used for compounds that ionic or giant covalent.
To find the relative formula mass just add up the relative atomic masses (Ar) of all the ions in the formula unit.
Calculate the relative formula mass of CaF2 and CaCO3
CaF2=
In CaF2 there’s one Ca2+ ion got every 2- ions. Mr if CaF2= 40.1+(2x19)= 78.1
CaCo3=
In CaCo3 there’s one Ca2+ ion for each CO3 2-
Mr= 40.1+12+(3x16)=100.1
What is a mole?
measurement of amount of substance given in symbol n.
one mole is 6.02x1023 particles - the Avogadros constant
it doesn’t matter what the particles are - they can be atoms, molecules,electrons,ions etc.
eg. 2Mg+O2-> 2MgO
2 atoms of magnesium react with 1 molceule of oxygen to make 2 molceules of magnesium oxide
2 moles of magnesium react with 1 mole of oxygen molecules to make 2 moles of magnesium oxide.
What is the formula for finding the number of moles from the number of atoms or molecules?
IF you have 1.50x10^24 carbon atoms how many moles of carbon is this?
Number of moles= number of particles you have/number of particles in a mole
moles= 1.50x10^24 / 6.02x10^23 = 2.49 moles
What is molar mass?
What is the unit for molar mass?
Find the molar mass for Ni(OH)2
Molar mass, M is the mass of one mole of something. Molar mass has the same numerical value as the relative molecular mass, Mr or relative formula mass.
The unit is gmol-1
Ni(OH)2= 58.7+ (2x(16+1))=92.7
M= 92.7 gmol-1 (1 mole of Ni(OH)2 weighs 92.7g)
What formula connects the molar mass of a substance to the number of moles of the substance you have?
`moles = mass of substance/ molar mass
mr mol lives under ground
How many atoms are in 1 mole of Fe?
6.02x1023
Find the molar mass of MgSO4
24.3+32.1+16x4= 120.4gmol-1
How many moles of sodium nitrate are present in 212.5g of NaNO3?
moles=mass/mr
212.5/85=2.5 moles
How many moles of zinc chloride are present in 15.5g of ZnCl2?
MOLES=MASS/MR
12.5/136.4=0.114 moles
what is the mass of 0.25 moles of MgCO3?
mass= molesxMr
21.075g=0.25x (84.3)
How many O2 molecules are in 82.1g of oxygen?
M= 16+16 = 32gmol-1
number of moles= 82.1/32 = 2.565..mol
number of molecules= 2.565… x 6.02x10^23=1.54x10^24
a sample of pure magnesium sulfate, MgSO4, contains 3.56x10^24 atoms. What is the mass of the sample?
number of moles of atoms = 3.56x10^24 x 6.02x10^23
=5.913 mol
MgSO4 = 6 atoms
moles of MgSO4 (using moles you have/moles in compound) = 5.913/6 = 0.985…
M(MgSO4) = 120.4gmol-1 mass = 0.985... x 120.4 = 119g is the mass of the sample
what is molar gas volume?
units?
if temperature and pressure stay the same, one mole of any gas always has the same volume - this is the molar gas volume
units: dm3mol-1
For molar gas volume, what are the values for room temperature and pressure?
temperature= 298K
pressure=100k
molar gas volume=24dm3mol-1 or 24,000cm3.mol-1
Give the 2 formulas for working out the number of moles in a volume of gas - ONLY USE THEM FOR R.T.P!
ONLY USED FOR R.T.P
number of moles= volume in dm3 / 24
OR
number of moles= volume in cm3 / 24,000
How many moles are there in 6.0dm3 of oxygen gas at R.T.P?
number of moles = 6.0 / 24
=0.25 moles of oxygen molecules
What volume, in cm3, does 0.020 moles of hydrogen gas occupy at r.t.p?
Rearrange the formula to find volume by multiplying both sides by 24,000
volume= number of moles x 24,000
=0.020x24000 = 480cm3
What is the ideal gas equation and when is it used?
What are the values?
The ideal gas equation is used when it’s not always room temperature and pressure:
pV=nRT
p=pressure (Pa)
v=volume (m3)
n=number of moles
R=the gas constant 8.314jk-1mol-1
T= temperature (K) just add the celsius degrees to 273
Rules for using the ideal gas equation
- if given values in different units from the one in the equation you need to convert them
- if pressure is given in kPa you convert it to Pa by x1000
- if temperature is given in °C, you add 273 to vobert it to K
- if volume is given in cm3 you multiply it by 10^-6
- if volume is given in dm3 you multiply it by 10^-3
At what pressure would 0.400 moles of argon gas occupy 0.0100m3 at 298K?
rearrange formula to find pressure by dividing both sides by V
p=nRT/V = 0.400x8.314x298 / 0.0100 = 99,100 Pa
How many moles are there in 0.0600m3 of hydrogen gas, at 283K and 50,000 Pa?
Rearrange the equation to find the number of moles (divide both sides by RT)
n=pV/RT =50,000 x 0.0600 / 8.314x283
=1.28 moles 3sf
what volume would 2.00 moles of argon gas occupy at 27.0°C and 100kPa?
Put all values into correct units: T=27+273= 300K p= 100kPa=100,000Pa now rearrange equation to find volume by diving both sides by pressure v=nRT/p = 2.00x8.314x300 / 100,000 =0.0499m3 3sf
combined calculation:
At a temperature of 60°C and a pressure of 250kPa, a gas occupied a volume of 1100cm3 and had a mass of 1.59g. Find its relative molecular mass.
Temperature, pressure and volume has been given so moles need to be calculated.
n= pV/RT (250x10^3) x (1.10x10^-3) / 8.314 x 333 = 0.0993… moles
Molar mass = mass/number of moles
1.59/0.0993…
=16.0gmol-1
so relative molecular mass is also 16.0
How many moles are there in 2.4dm3 of carbon dioxide gas at r.t,p?
2.4/24 = 0.1 moles
How many moles are there in 0.65dm3 of carbon monoxide gas at r.t.p?
0.65/24=0.027 moles
How many moles are there in 250cm3 of sulfur dioxide gas at r.t.p?
250/24,000= 0.010 moles
What volume, in dm3, does 0.21 moles of HCl gas occupy at r.t.p?
volume = 0.x21 x 24 = 5.04dm3
What volume, in dm3 does 1,1 moles of fluorine gas occupy at r.t.p?
volume = 1.1x24= 26/4dm3
What volume in cm3 does 0.028 moles of argon gas occupy at r.t.p?
volume = 0.028x24,000 = 672cm3
How many moles are there in 0.04m3 of oxygen gas at a temperature of 350K and a pressure of 70,000 Pa?
n=pV/RT
=(70,000 x 0.04) / (8.314 x 350) =0.96 moles
What volume would 0.65 moles of carbon dioxide gas occupy at a temperature of 280K and a pressure of 100,000 Pa?
V=nRT/p
=(0.65 x 8.314 x 280) / 100,000 = 0.015m3
How many moles are there in 0.55dm3 of nitrogen gas at a temperature of 35°C and a pressure of 90,000 Pa?
0.55dm3 = 0.55 x 10^-3m3 35°C= 308K n=pV/RT =(90,000 x (0.55 x 10^-3)) / (8.314 x 308) =0.019 moles
At a pressure of 110,00 Pa, 0.05 moles of hydrogen gas occupied a volume of 1200cm3. What was the temperature in °C.
1200cm3= 1200x10-6m3 = 1.2x10-3m3
T=pV/nR
= (110,00 x 91.2 x 10^-3)) / (0.5 x 8.314) = 317.5 K
317.5K = 9317.7-273) °C=44.5
What volume would 0.75 moles of helium gas occupy at a temperature of 22°C and a pressure of 75kPa?
75kPa = 75,000 Pa 22°C = 295K
V=nRT/p
=(0.75 x 8.314 x 295) / 75,000 = 0.025m3
At a temperature of 300K and a pressure of 80kPa a gas had a volume of 1.5dm3 and a mass of 2.6g.
Find its relative molecular mass.
80kPa= 80,000 Pa 1.5dm3= 1.5x10^-3m3 n=pV/RT = (80,000 x (1.5x10^-3)) / (8.314 x 300) =0.048 moles molar mass = mass/moles =2.6/0.048 = 54gmol-1 RELATIVE MOLECULAR MASS =54
A student had a sample of neon gas, Ne.
They heated it to 44°C.
At this temperature the gas had a volume of 0.003m3.
If the pressure was 100kPa, what was the mass of the neon gas?
44°C= 317K 100kPa= 100,000 Pa n=pV/RT =(100,000 x 0.003) / (8.314 x 317) =0.114 moles Molar mass of Neion = 20.2 mass= number of moles x molar mass =0.114x 20.2 =2.30g
What is concentration?
What are the units?
the concentration of a solution is how many moles/how many grams of something are dissolved per 1dm3 of solution.
The units are moldm^-3 or gdm^-3
a solution that has more moles per dm3 than another is more concentrated, with less = dilute.
What is the formula regarding moles with concentration
number of moles= concentration x volume (in cm3) / 1000
OR
number of moles = concentration x volume (in dm3)
formula triangle moles=conc x vol
How many moles of lithium chloride are present in 25cm3 of a 1.2moldm^-3 solution of LiCl?
Number of moles= concentration x volume (in cm3) /1000
1.25 x 25 / 1000 = 0.030 moles
A 0.50 mol dm-3 solution of zinc sulfate contains 0.080 moles of ZnSO4, what volume does the solution occupy?
Rearrange the formula to find volume (divide both dsides by volume):
volume (in dm3) = number of moles / concentration
=0.080/0.50 = 0.16dm3
combo calc
What mass of sodium hydroxide needs to be dissolved in 50cm3 of water to make a 2.0 moldm^-3 solution?
You have concentration and volume so work out moles.
moles = concentration x volume (cm3) / 1000
=2.0x50/1000 = 0.10 moles of NaOH
Use this to work out mass using moles=mass/molar mass
molar mass, m, of NaOH= 23+16+1 = 40gmol-1
mass= number of moles x M = 0.10 x 40 = 4.0g
How many moles of potassium phosphate are present in 50cm3 of a 2moldm-3 solution
50/100= 0.05dm3
0.05 x 2 = 0.1 mol
How many moles of sodium chloride are present in 0.5dm3 of a 0.08moldm3 solution?
0.5 x 0.08 = 0.04 moles
the molecular formula of CoBr2, what mass of cobalt bromide would you have to dissolve in 30cm3 of water to make a 0.5moldm-3 solution?
n=c x v 0.03 x 0.5 =0.015 moles mass=molxmr 0,015 x 218.7 = 3.28g
a solution is made by dissolving 4.08g of a compound in 100cm3 of pure water. The solution has a concentration of 1.2 moldm^-3.
What is the molar mass of the compound?
n=c x v
0.1 x 1.2 = 0.12
molar mass = mass/mr = 4.08/0.12 = 34gmol-1
DEFINE empirical formula
the smallest whole number ratio of atoms of each element in a compound
DEFINE molecular formula
gives the numbers of atoms of each type of element in a molecule
How can you calculate the molecular formula?
if you know the empirical formula and the molecular mass of a compound
- Find the empirical mass
- divide molecular mass by empirical mass
- multiply empirical formula by that number to find the molecular formula
What happens during a chemical reaction?
- no atoms are created or destroyed
- the atoms that are reactants are rearranged to form the atoms that are products
What are the ‘species’ in equations?
the type of particle taking part in the reaction
- electron
- molecule
- ion
What do the state symbols show us?
tells the physical state the species are in
How do you balance an equation? Balance C2H6O (g) + O2 --> CO2(G) + H20(g)
- write out the equation :
C2H6O (g) + O2 –> CO2(G) + H20(g) - check that the reactants and products are balanced
3.balance them by using the RP table
4.Rewrite the balanced equation
C2H6O (g) + 3O2 –> 2CO2(G) + 3H20(g)
How to write ionic equations?
for the reaction between Sodium Chloride and Silver Nitrate.
- Write out the original balanced equation
NaCl(aq) + AgNO3(aq) —–> AgCl(s) + NaNO3(aq)
2.Re-write the equation to show which components dissociate into ions. ONLY THE AQ DISSOCIATE INTO IONS
Na+ + Cl- + Ag+ + NO3- —–> AgCl + Na+ + NO3-
- Cancel out any spectator ions (ions that appear in both the reactants and the products) to produce the net ionic equation:
Cl- + Ag+ ——> AgCl
For Questions on empirical formula and molecular formula refer to page 53 in the CGP revision guide.
!!!
what’s the rule with ion formation with metals
metals tend to form ions with a charge taht is the same as their group number
what’s the rule with ion formation with non metals?
non metals form ions with a charge that’s equal to their group number minus 8
which elements form 1+ ions?
group 1 elements lose 1 electron to form 1+ ions
which elements form 2+ ions?
group 2 elements lose 2 electrons to form 2+ ions
what elements form 2- ions?
group 6 elements gain 2 electrons to form 2- ions
which elements form 1- ions?
group 7 electrons gain 1 electron to form 1- ions
what charged ions is lithium likely to form?
Li+
what charged ions is calcium likely to form?
ca2+
what charged ion is sulfur likely to form?
2-
what charged ion is fluorine likely to form?
F-
list the names of the molecular ions you need to know
nitrate carbonate sulfate hydroxide ammonium
what’s the formula for nitrate
NO3-
what’s the formula for carbonate
CO3^2-
what’s the formula for sulfate
SO4^2-
what’s the formula for hydroxide
OH-
what’s the formula for ammonium
NH4+
what’s the formula of zinc ion?
Zn2+
what’s the formula for Silver ions?
Ag+
when are ionic compounds made?
when positive and negative ions bond together by ionic bonding
what’s the ruling on charges in ionic compounds?
the charges must always balance out to 0
e. g. NaCl Na+ + Cl-
e. g. MgCl2 Mg2+ Cl- x2
what’s the formula for potassium sulfate?
K = group 1 so +1
sulfate ion = So4^2-
for every 1 sulfate ion you need to K ions
so formula
K2SO4
what’s the formula of silver nitrate?
Ag = +1
nitrate ion= NO3-
balances so AgNO3
what are acids?
acids are proton donors
what happens when an acid is mixed with an aqueous solution
the acid will release H+
what do hydrogen atoms contain
only one proton and one electron, do a H+ which has lost the electron is just a proton
what are bases
bases are proton acceptors that grab H+ ions
what happens when an alkali is mixed with an aqueous solution
they release OH- ions
what are alkalis
bases that are soluble in water
give the names of all 4 acids and their formulas in order of strength
Hydrochloric Acid HCl
Sulfuric Acid H2SO4
Nitric Acid HNO3
Ethanaoic Acid CH3COOH
give the names of all 3 bases and their formulas in order of strength
Sodium Hydroxide NaOH
Potassium Hydroxide KOH
Ammonia NH3
which base is unique and why is it unique? give the formula to show why
- Ammonia NH3 (aq nh3 is an alkali)
- accepts a proton from an acid to form an ammonium ion, then forms an ammonium salt.
writing equations with anmoniUM ions (nh4+) is trickier because ammonia doesn’t directly make OH- ions, when ammonia reacts with water it produces an ammonium ion and a hydroxide ion:
NH3 (aq) + H2O = NH4+ (aq) + OH- (aq)
what’s important to know about the reaction between an acid and water or a base and water?
the reaction is reversible so at any point in time both the forwards and backward reaction will be happening
what’s the generic equation for the reaction of an acid with water?
HA + H20 = H3O+ + A-
both of these reactions are occurring:
HA + H20 = H3O+ + A-
H3O+ + A- = HA + H20
what’s the generic equation for the reaction between a base and water?
B + H20 = BH+ + OH-
both of these reactions are occurring:
B+ H2O = BH+ + OH-
BH+ + OH- = B+ + H2O
